Conventionally, in methods for producing a toner, wet methods including polymerization methods such as the suspension polymerization method, the emulsion polymerization method, and the dispersion polymerization method, solution suspension methods and so on have been employed since the shape of particle diameter, the diameter of particles and the particle size distribution can be easily controlled. Particularly, among the wet methods, the suspension polymerization method is preferably employed since high-quality images can be formed upon printing.
In the method for producing a toner by the suspension polymerization method, which is a representative wet method, a toner is produced through various steps including (1) preparing a polymerizable monomer composition, (2) forming droplets, (3) polymerization, and (4) washing, filtering, dehydrating and drying. Thus, from the viewpoint of improving productivity, reduction in number of production steps and simplification of facilities are considered.
Recently, in the drying step of the wet methods, from the viewpoint of improvement in energy efficiency of dryers, the percentage of moisture content of an object to be dried in a dryer (colored resin particles in a wet state (wet cake)) is required to be sufficiently reduced preliminarily before the drying step without decreasing the productivity of a toner, and various attempts are made.
Japanese Patent Application Laid-Open (JP-A) No. 2007-58201 discloses a method for producing a toner, wherein a series of steps including washing, filtration and dehydration of a slurry containing toner particles produced in a liquid dispersion medium is performed using a filter cloth intermittent motion type belt filter equipped with a squeezing ventilation means to decrease the percentage of moisture content of the wet cake obtained thereby.
Also, JP-A No. 2008-112153 discloses a method for producing a toner, wherein a series of steps including solid-liquid separation, filtration and dehydration of a toner particle dispersion liquid produced in an aqueous dispersion medium is performed using a filter cloth intermittent motion type belt filter equipped with a ventilation means for dehydration by ventilation and a sealing means for sealing the gas subjected to ventilation to decrease the percentage of moisture content of the wet cake obtained thereby.
Though JP-A No. 2007-58201 discloses the result that a wet cake with low percentage of moisture content was obtained by the method for producing a toner of JP-A No. 2007-58201, there is a problem that the slurry is not uniformly supplied on the filter cloth since the filter cloth runs intermittently. Uneven washing of the wet cake can be presumed.
Also, though JP-A No. 2008-112153 discloses the result that a wet cake with low percentage of moisture content was obtained by the method for producing a toner of JP-A No. 2008-112153, there is a problem that the rate of solid-liquid separation decreases since a sealing part needs to be provided as a separate part, which makes the sealing mechanism complicated. Thus, the productivity of the conventional methods for producing a toner cannot reach the level required recently, and further study is required.